1. Field of the Invention
The present disclosure relates to a technique for discharging liquid droplets from a liquid droplet discharge head.
2. Description of the Related Art
There is an ink jet recording apparatus as an example of image forming apparatus such as a printer, a facsimile machine, a copying machine, and a multifunction peripheral including the printer, the facsimile machine, and the copying machine in a combined manner.
In recent years, in order to cause an ink jet recording apparatus to print at a higher speed, a large-sized drop having a large amount of ink droplet are required to be ejected in a stable manner with high frequency driving.
In order to obtain preferable gradation property, a large-sized drop and multiple types of ink droplets of which amounts of ink droplet are less than that of the large-sized drop are required to be ejected independently at the same time. In addition, these multiple types of ink droplets are required to be ejected in a stable manner with high frequency driving.
In order to obtain preferable image quality, it is required to eject multiple types of ink droplets in a stable manner with high frequency driving, even when low viscosity ink is used.
Furthermore, because of the reduction in the sizes of nozzle holes and liquid chambers due to higher density integration of the nozzles, the amount of discharged ink droplet per pulse is decreased, and therefore, it is necessary to configure a driving waveform having many pulses in order to obtain a large-sized drop.
However, when the number of pulses of the driving waveform increases in order to obtain the large-sized drop, the large-sized drop is more likely to be affected by variation in an acoustic natural period Tc of a pressure chamber, resulting in increase of variation in the ejection speed and the amount of ink droplet for each channel.
Under such background, for example, Japanese Patent Laid-open No. 2003-175601 discloses a technique for suppressing variation of the acoustic natural period Tc.
In Japanese Patent Laid-open No. 2003-175601, a driving waveform is configured such that, in the acoustic natural period Tc of the ink droplet discharge head, the pulses are arranged in such order that the pulse intervals gradually become closer to the acoustic natural period Tc, and a pulse longer than the acoustic natural period Tc and a pulse shorter than the acoustic natural period Tc are arranged alternately. With the configuration of the driving waveform, the variation of the speeds of the ink droplets adjacent to each other are in the opposite direction, so that the variation of the acoustic natural period Tc is cancelled.
However, in the configuration of the driving waveform described in Japanese Patent Laid-open No. 2003-175601 explained above, when the number of pulses is increased in order to increase the amount of ink droplet, a pulse out of a resonance peak is frequently used in the former half of the waveform, and this may result in reduction of the stability of the discharge. Furthermore, a pulse close to the resonance peak is frequently used in the latter half of the waveform, and therefore, the residual vibration is amplified more than necessary. Thus, the effect of the residual vibration is increased until a subsequent discharge cycle, and this may reduce the stability of discharge.
There is a need for an image forming apparatus that enables preferable discharge stability.